Television receivers for multiple color television broadcasting systems including PAL and NTSC incorporate a color system determination circuit for automatically determining the type of color television broadcast signal received.
The Japanese Laid-open Patent No. S63-131680 discloses one such type of color system determination circuit.
The color system determination circuit of the prior art employs two clock oscillators for determining color systems. Specifically, this color system determination circuit has two clock oscillators for producing two different color subcarrier frequencies. These two clock oscillators are switched for oscillation, and the broadcasting system of the television input signal is checked and determined based on these oscillation signals. The prior art may require a certain period of time for making a determination.